Method for manufacturing a preform for composite materials

A method for manufacturing a preform having a non-developable shape comprising a plurality of superposed reinforcing layers of fibers to form a part made of composite materials having a final shape comprising a final global radius of curvature about a longitudinal axis and curved segments forming folding radii connecting substantially straight segments in at least one longitudinal section, the method comprising:

• depositing successive layers on a surface of a draping tool giving an initial shape substantially of revolution having an initial global radius of curvature about the longitudinal axis, the initial shape including an open contour about the longitudinal axis;
• and
• deploying the preform by increasing the initial global radius of curvature up to the final global radius of curvature in order to close the folding radii of the curved segments.